Varying water deficit stress (WDS) tolerance in grain amaranths involves multifactorial shifts in WDS-related responses

In this study, water deficit stress (WDS)-tolerance in several cultivars of grain amaranth species (Amaranthus hypochondriacus [Ahypo], A. cruentus [Acru] and A. caudatus [Acau]), in addition to A. hybridus (Ahyb), an ancestral amaranth, was examined. Ahypo was the most WDS-tolerant species, whereas Acau and Ahyb were WDS-sensitive. Data revealed that the differential WDS tolerance observed was multifactorial. It involved increased proline and raffinose (Raf) in leaves and/ or roots. Higher foliar Raf coincided with induced Galactinol synthase 1 (AhGolS1) and Raffinose synthase (AhRafS) expression. Unknown compounds, possibly larger RFOs, also accumulated in leaves of WDS-tolerant amaranths, which had high Raf/ Verbascose ratios. Distinct nonstructural carbohydrate (NSC) accumulation patterns were observed in tolerant species under WDS and recovery, such as: i) high Hex/ Suc ratios in roots coupled to increased cell wall and vacuolar invertase and sucrose synthase activities; ii) a severer depletion of starch reserves; iii) lower NSC content in leaves, and iv) higher basal hexose levels in roots which further increased under WDS. WDS-marker gene expression patterns proposed a link between amaranths WDS tolerance and abscisic acid-dependent signaling. Results obtained also suggest that AhTRE, AhTPS9, AhTPS11, AhGolS1 and AhRafS are reliable gene markers of WDS tolerance in amaranth.\n\nHighlightDifferential water deficit stress tolerance in grain amaranths and their ancestor, Amaranthus hybridus, is a multifactorial process involving various biochemical changes and modified expression patterns of key stress-related genes.